Papers by Author: P.V. Datta Prasad

Abstract: Ultrasonic velocity measurements are carried out on four nOm compounds viz., N-(p-n-methoxy and ethoxy benzylidene)-p-n-dodecyl and tetradecyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. The first three compounds exhibit mono variant nematic phase while the last compound exhibits nematic and smectic-A phases with variable thermal ranges. The temperature dependence of sound velocity, U shows minima at the isotropic-nematic and nematic-smectic-A transitions. In conjunction with the density data of these compounds, the thermo acoustic parameters such as adiabatic compressibility (β_ad), the molar sound velocity (Rao’s number) (R_n), molar compressibility (W), molecular free length (L_f) and available volume (V_a) are estimated. In addition the intermolecular free length (L_f) is estimated in three different ways employing density and ultrasonic velocity data. The results are compared with the data available in literature of other compounds.

Abstract: Liquid crystal polymers are the low cost, flexible structured and low weight substrate materials for making antennas. Liquid crystal polymers are excellent dielectric materials having good electrical, mechanical properties which suites in the application of microstrip patch antennas. In this paper liquid crystal polymer with dielectric constant 3.16 is used as substrate material for planar dipole antenna designed to operate at 2.4 GHz. Ansoft-HFSS software is used to simulate the proposed model and obtained the return loss, input impedance, 3D-gain, 2D-gain total, radiation patterns in E and H planes, E-field and H-field distribution results.

Abstract: The liquid crystalline compounds viz, N-(p-n-decyloxybenzylidene)-p-n-octadecyl aniline, 10O.18, N-(p-n-octadecyloxybenzylidene)-p-n-octadecylaniline, 18O.18, (p-n-biphenylbenzylidene) -p-n-octadecylaniline, PB18A and terephthalyidene-bis-p-n-octadecylaniline, TB18A have been synthesized for the first time and the characterization is carried out using thermal microscopy (TM) attached with a hot stage and differential scanning calorimeter (DSC). All the four compounds exhibit a variety of phase variants such as isotropic to smectic-F (Iso-SmF) in 10O.18, isotropic to smectic-F (Iso-SmF) in 18O.18, isotropic to smectic-A to smectic-B (SmA-SmB) in PB18A and isotropic to smectic-C to smectic-I to smectic-F (Iso-SmC-SmI-SmF) in TB18A.

Abstract: The nature of the phase transitions across isotropic–nematic (IN) and nematic–smectic-A (N-SmA) are carried out using density measurements in N-(p-n-ethoxy benzylidene)-p-n-pentyl aniline, 2O.5, N-(p-n-methoxy benzylidene)-p-n-pentyloxy aniline, 1O.O5, N-(p-n-ethyl benzylidene)-p-n-dodecyl aniline, 2.12 and N-(p-n-butyl benzylidene)-p-n-dodecyl aniline, 4.12. The compounds exhibit IN, IN, IN and INSmA phase sequences respectively with varying thermal ranges suitable for the study of birefringence. The birefringence studies are carried out using Newton’s rings and wedge techniques which provide δn = (n_e - n_o) (the birefringence) n_e, and n_o respectively. The orientational order parameter, S is evaluated (i) directly from δn and Δn (the birefringence in perfect order), independent of the local field that the nematic molecule experiences and (ii) from molecular polarizabilities estimated from n_e, n_o and density values assuming isotropic as well as anisotropic field that the nematic molecule experiences. The estimated order parameter from the different techniques is compared with one another and with the literature data.

Abstract: Refractive indices measurements are carried out in four alkoxy benzylidene anilines viz., N-(p-n-methoxy and ethoxy benzaldehyde)-p-n-dodecyl and tetra decyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. First three compounds exhibit monovariant nematic phase while the last compound exhibits nematic and SmA phases with variable thermal ranges. The molecular polarizabilities are calculated from the refractive indices and the density using the well known internal field models by Vuks and Neugebauer. The molecular polarizability anisotropy is estimated from the Lippincott δ-function model as well as molecular vibrational methods. The order parameter is estimated using a) from the Haller’s extrapolation from molecular polarizabilities, b) from the scaling factors obtained from the equations by Vuks and Neugbeaur and c) directly from the birefringence - a method developed by Kuczynski et al without considering any internal field model to the liquid crystal molecule. The results evaluated from these methods are compared from one another and the limitations of the methods used are discussed.

Abstract: The refractive indices measurements are carried out using a modified spectrometer connected with wedge shaped cell and also the direct measurement of birefringence,δn obtained from Newton’s rings method with an indigenous setup for the liquid crystalline compounds p-n-(phenyl benzylidene)-p-n-alkyl and alkyloxy anilines, PBnA and PBnOA compounds. The molecular polarizabilitiy anisotropy (α_|| - α_⊥) is calculated for these compounds from different methods such as Lippincott δ-function model, molecular vibration method, Haller’s extrapolation method and scaling methods respectively. Further, the estimation of the molecular polarizabilities α_e and α_o are done from the isotropic Vuks and anisotropic Neugebauer models. The order parameter directly calculated from ∆n employing the method developed by Kuczynski is compared with the order parameter estimated from the different models using molecular polarizabilities.

Abstract: Synthesis, characterization and phase transition studies (Dilatometry) have been carried out on three mesomorphic Schiff base compounds viz., N-(p-n-pentyl benzylidene)-p-n-hexadecyloxy aniline, 5.O16, N-(p-n-pentyloxy benzylidene)-p-n-hexadecyloxy aniline 5O.O16 and N-(p-n-pentyl benzylidene)-p-n-hexadecyl aniline, 5.16. The liquid crystalline phase identification and the phase transition temperatures have been carried out using SDTECHS polarising microscope attached with temperature controller with accuracy of ± 0.1 °C and for the conformation of the phase identification and the textures observed are compared with the standard textures. Further, the phase transition temperatures and the corresponding heats of transition across the phase transitions are recorded using DSC (Perkin Elmer). The characterization studies reveal that these compounds exhibit NG, N and A phase variants respectively. The nature of the phase transitions are studied through density results using dilatometric technique. The phase transitions exhibit first order nature in all the cases as expected. The results are discussed in the light of the body of the data available on other Schiff base compounds and on 5O.16.